1. Field of the Invention
The present invention relates to an implant and, more particularly, to a bone implant that can be implanted into a bone.
2. Description of the Related Art
Generally, biting and chewing functions will be adversely affected if a tooth defect resulting from either aging or accidental impact is not restored. In severe cases, after effects, including forward declination of a tooth behind the location of a missing tooth, shrinkage of bone, and a change of the face shape, occur. Among various methods for tooth restorations, tooth implantation is becoming more and more popular due to the advantages of the lack of harm to natural teeth on two sides of the location of the missing tooth, of being easy to clean, of not causing feeling of a foreign substance, and of an aesthetic appearance after implantation.
Tooth implantation includes implanting a dental implant made of a medical grade material (such as titanium or ceramic) into an alveolar bone of a patient in a surgery. After bone integration, a dental crown is mounted to the tooth implant to restore the tooth of the patient for chewing and aesthetic purposes. The dental implant includes an implant and an abutment. The implant is implanted into the alveolar bone of the patient, the abutment is mounted to an end of the implant, and the dental crown is fixed to the abutment.
To assure reliably fixing of the abutment to the end of the implant, common dental implants nowadays generally have three pieces. Specifically, a blind hole extends axially from an end of the implant, and the abutment includes an axially extending bore. After the abutment is inserted into the blind hole of the implant, an abutment screw extends through the bore of the abutment, with an end of the abutment screw engaged in the abutment, and with the other end of the abutment screw extending out of the abutment and extending into and tightened in the blind hole of the implant by thread engagement, achieving secure coupling between the implant and the abutment.
However, there is no retaining or positioning structure between the abutment and the implant before the abutment is securely fixed in the blind hole of the implant by the abutment screw. Thus, the abutment is apt to fall out of the blind hole of the implant in a tooth implantation surgery of an upper tooth, causing inconvenience to the surgery and adversely affecting surgery efficiency. In severe cases, the abutment falls on and stimulates the tongue of the patient, such that the patient swallows the abutment, resulting in medical disputes.
FIG. 1 shows a dental implant 9 including an implant 91, an abutment 92, and an abutment screw 93. A blind hole 911 extends axially from an end of the implant 91, forming an insertion portion 912 and a locking portion 913 in an interior of the implant 91. An annular flange 914 is formed on an inner periphery of the insertion portion 912. The locking portion 913 is closer to a closed end of the blind hole 911 than the insertion portion 912. The abutment 92 includes an implant coupling portion 921, a connection portion 922, a crown coupling portion 923, and an axially extending bore (not shown), with the implant coupling portion 921, the connection portion 922, and the crown coupling portion 923 connected to each other in the axial direction. The implant coupling portion 921 includes an annular groove 924 adjacent to a free end thereof. A plurality of resilient fingers 925 is provided between the annular groove 924 and the free end of the implant coupling portion 921. Each resilient finger 925 includes an outwardly protruding arcuate face. A notch 926 is formed between two adjacent resilient fingers 925. The resilient fingers 925 elastically deform when subjected to a radially-pressing external force and return to their initial position when the external force vanishes. An example of such a dental implant is disclosed in U.S. Pat. No. 7,338,286 (EP 1419746 B1).
In use of the dental implant 9, the implant 91 is implanted into an alveolar bone of a patient, and the implant coupling portion 921 of the abutment 92 is then inserted into the insertion portion 912 of the implant 91. During axial movement of the implant coupling portion 921 of the abutment 92 into the blind hole 911, and when the resilient fingers 925 come in contact with the annular flange 914, the annular flange 914 causes elastic deformation of the resilient fingers 925 and presses the resilient fingers 925 radially inward. After passing through the annular flange 914, the resilient fingers 925 return to their initial position, and the annular groove 924 of the abutment 92 is aligned with the annular flange 914. By abutting the resilient fingers 925 against a side of the annular flange 914, the whole abutment 92 can engage with the implant 91 and, is, thus, less likely to disengage from the implant 91 in the axial direction. Finally, the abutment screw 93 extends through the bore of the abutment 92 to fix an end of the abutment screw 93 in the abutment 92. The other end of the abutment screw 93 extends out of the abutment 92 and is tightened to the locking portion 913 of the implant 91 by thread engagement, achieving secure coupling between the implant 91 and the abutment 92.
When the abutment 92 of the dental implant 9 is being mounted, the abutment 92 and the implant 91 are engaged with each other before the abutment screw 93 is tightened, avoiding the abutment 92 from disengaging from the implant 91 after installation. However, it is difficult to form the delicate structures including the annular grooves 924, the resilient fingers 925 with outwardly protruding arcuate faces, and the notch 926 between two adjacent resilient fingers 925, because the size of each component of the dental implant 9 is relatively small. Thus, manufacturing of the abutment 92 becomes more difficult and has a low yield. Furthermore, formation of the annular flange 914 in the blind hole 911 of the implant 91 causes changes in the diameter of the blind hole 911 from the closed end to the open end thereof. Specifically, processing of the blind hole 911 is not as easy as the case of a blind hole having increasing diameters from an end to the other end. Rather, the diameter of the blind hole 911 is increased and then reduced and then enlarged, which requires special cutters and/or many processing procedures to form the desired shape. Thus, the implant 91 has the same disadvantages of difficult manufacturing and low yield. Furthermore, metal fatigue and breakage of the dental implant 9 are apt to occur clinically due to repeated coupling of the abutment 92 and the implant 91 by an inexperienced practitioner. Overall, the coupling structure of the dental implant 9 is too complicated, causing difficulties and low efficiency in manufacturing as well as a low yield. As a result, the dental implant 9 has high manufacturing costs.
Furthermore, the avoidance of disengagement of the abutment 92 of the dental implant 9 from the implant 91 can only be achieved after the resilient fingers 925 have passed through the annular flange 914 of the implant 91 to a position in which the annular groove 924 of the abutment 92 is aligned with the annular flange 914. Namely, when the abutment 92 is being coupled to the implant 91, the abutment 92 is not always in an engagement relation with the implant 91. If the practitioner fails to couple the abutment 92 to the predetermined location in the implant 91, it is possible for the abutment 92 to fall out of the implant 91. Further, as mentioned above, the annular flange 914 of the implant 91 and the resilient fingers 925 of the abutment 92 are delicate structures such that the practitioner can not exactly feel the resilient fingers 925 have passed the annular flange 914 of the implant 91. Thus, the dental implant 9 can not provide the expected result of avoiding the abutment 92 from falling out of the implant 91. Further, the dental implant 9 has a weak structure and is apt to fatigue.